设A=1/2+1/3+1/4+1/5 B=1/2+1/3+1/4+1/5+1/6
原式=(1+A)×B-(1+B)×A
=B+A×B-A-A×AB
=B-A
=(1/2+1/3+1/4+1/5+1/6)-(1/2+1/3+1/4+1/5 )
=1/6
设A=1/2+1/3+1/4+1/5 B=1/2+1/3+1/4+1/5+1/6
原式=(1+A)×B-(1+B)×A
=B+A×B-A-A×AB
=B-A
=(1/2+1/3+1/4+1/5+1/6)-(1/2+1/3+1/4+1/5 )
=1/6